I wouldn't say no difference. Using all reservations for example would make it harder to complete the initial setup. I'm presuming that if you have a pool of one TB, you can't create three datasets, each with reservations of 500 GB.
Personally, I'd set a reservation on a low proportion of datasets if they are used for tasks that might break if they run out of space (a log repository). I'd use quotas for a majority of datasets to keep those tasks in check (limiting users / restricting the size of a TimeMachine backup).
What's your goal? Do you want to restrict a task? Or guarantee a task?